Blind people that see absolutely nothing are very much in the minority. Most blind people who truly cannot see experience flashes of light occasionally and also sense a different shade of darkness when they close the eyes.
This is an excellent starting point to describe the concept of colour using the senses of touch, taste and sound to help explain differences and the wide range of colour.
There are many things that are known facts that I cannot understand, no matter how hard I try I cannot grasp the concept. I can probably explain these facts in a satisfactory manner even though I can't grasp them myself. I can, however, believe those facts are in fact, factual.
In the same way it is important that blind people have the chance to accept that colour exists and understand the terms of reference when colour crops up in conversation, as it often does.
This amazing man was born without eyes and is talented artist. He is one of many so-called blind artists.
http://www.armagan.com/
I believe there is an ABer who is such a person.